Ultrasound waves are utilized in many different fields, typically as a tool to penetrate a medium to measure its reflection signature. In medicine, imaging ultrasound devices are usually used for diagnostic medical imaging of internal organs, muscles, tendons and even fetus inside the uterus [1]. Other existing medical applications include monitoring different organs, nerve stimulation, wound healing and rehabilitation [2], [4]-[9].
Traditional ultrasound imaging devices are capable of providing sophisticated live images and enable extraction of characteristic features using advanced signal processing techniques. However, they are generally large, stationary and expensive. Moderate size imaging devices with limited mobility, such as computer-on-wheels systems, are also available with performance generally similar to the larger systems [10]-[11]. More recently, there have been a few introductions of handheld ultrasound imaging devices, such as the GE Vscan [12] and Acuson P10 [13] that feed the need of on-the-go applications. However, none of these devices are wearable or nonintrusive. In a wide range of medical ultrasound diagnostic applications, such as fetal heartbeat monitoring, the ability to continuously monitor the heartbeat is more significant than producing an image of the heart. Fetal heartbeat sensing devices, using ultrasound Doppler, are available in large-size, medical-grade instruments [14] and lower cost, consumer handheld ones [15]-[16]. However, these current solutions are not wearable (due to size) and therefore do not enable continuous monitoring without interfering with the subject's regular activities. They are also expensive compared to the price point possible for the patch-type device disclosed here.
Current therapeutic and rehabilitation ultrasound machines are stationary and require regular visits by the patient due to the gradual and progressive nature of the treatment; sometimes for duration of few months. Patients with known lesions in the carotid artery should also visit the hospital for taking the ultrasound and being monitored regularly depending on the risk factors. Such monitoring also occurs after surgery.
For decades, ultrasound machines were only available in stationary locations in hospitals and were operated by trained technicians for diagnostic applications. Today however, portable and handheld diagnostic ultrasound machines enable doctors to examine their patients at the point of care, whether at bedside or an accident scene [17]. Other types of applications include therapeutic devices of small size that can either be applied by a therapist [12], [18] or at home by the patient for physical therapy, reducing healing time and rehabilitation, or just to reduce pain [19].
The importance of a lighter weight, user friendly and inexpensive ultrasound device for such applications is compelling [7]-[9]. With continuous monitoring of the arteries with an easy-to-apply, wirelessly-powered adhesive patch, the patient can be monitored more closely all the time, eliminating the need for frequent visits to the hospital. In addition, such a device can save lives by detecting the onset of stroke as changes in the shape and size of the lesion is observed. An ultrasound patch, similar in form factor to a medical adhesive patch (e.g., an appropriately-sized BandAid), can be worn by a subject without interfering with the subject's routine activities, allowing continuous monitoring or therapy. The ultrasound data can be recorded on the patch for subsequent download/transmission and/or transmitted in real time (wirelessly) to a nearby portable device, such as a mobile phone, personal digital assistant, or personal computer. In addition to serving as a relay station to (wirelessly) transmit the acquired data to a network of backend servers, analytics and visualization can be made available on the portable device for the benefit of the subject. A network of backend servers usually supports the healthcare providers for further analysis of the data/information or for archiving of the data/information in electronic records. Benefits of such electronic recording, analysis, transmission, and archiving of ultrasound signals is compelling in many settings, including ambulatory, home, office, hospital, and trauma care.